Evaluating Partisan Gerrymandering in Wisconsin

Journal Article

We examine the extent of gerrymandering for the 2010 General Assembly
district map of Wisconsin. We find that there is substantial variability in the
election outcome depending on what maps are used. We also found robust evidence
that the district maps are highly gerrymandered and that this gerrymandering
likely altered the partisan make up of the Wisconsin General Assembly in some
elections. Compared to the distribution of possible redistricting plans for the
General Assembly, Wisconsin's chosen plan is an outlier in that it yields
results that are highly skewed to the Republicans when the statewide proportion
of Democratic votes comprises more than 50-52% of the overall vote (with the
precise threshold depending on the election considered). Wisconsin's plan acts
to preserve the Republican majority by providing extra Republican seats even
when the Democratic vote increases into the range when the balance of power
would shift for the vast majority of redistricting plans.